1. Field of the Invention
The present invention relates to an apparatus for making real time evaluations of pollutants in the exhaust gas emissions of motor vehicles, and is particularly, but not exclusively, applicable to the measurement of emissions from near-zero level emissions vehicles. It further relates to the comparison of the levels of contaminants in the exhaust gas emissions of vehicles to the level of pollutants in the ambient air through which the vehicle is travelling.
2. Description of Related Art
Automobile exhaust is a major air pollutant, contributing to increased health concerns and also such unappealing environmental conditions as smog. Los Angeles, well known for its brown haze, is of late only one of a number of major cities to deal with the problem of pollutants. In the fight to combat the deleterious effects of automobile exhaust pollutants, the federal government and many states have required emissions testing of automobiles. A more recent step has been to require automobile manufacturers to produce reduced and low level emissions vehicles. In response to government regulation, and also in the interest of producing reduced level of pollutants, several automobile manufacturers are providing reduced or near-zero emission vehicles to consumers. A necessary corollary of the innovative production of near-zero emission vehicles has been the need to produce pollutant measuring devices that will be able to demonstrate that the vehicles in question have in fact obtained a near-zero level of pollutants. Furthermore, pollution measuring devices may also be useful in vehicle development, such as in calibration of the engine control computer of a vehicle.
Historically, on-line gas analysis of engine exhaust emissions was not used, and vehicles were tested in a laboratory environment. The exhaust from the automobile was piped through a series of systems and collected in bags, and then later analyzed using such gas analysis techniques as chemilluminescence, flame ionization, and total hydrocarbon analysis. However, this process does not sample the ambient air encountered in actual driving conditions for comparison with the vehicle exhaust.
More recent technology advances have made Fourier transformer infrared (FTIR) spectrometric techniques available for use in gas analysis. For example, U.S. Pat. No. 4,928,015 discloses a method of using FTIR quality control techniques for analyzing multi-component constituency in gas emission flow. An FTIR spectrometer can provide simultaneous real-time concentration measurements of exhaust gas components, and is applicable for those gases which absorb infrared radiation in a sample because of the molecular oscillations and rotations. Those gases show a specific infrared absorption at different wavelengths resulting in typical spectra. All of the spectra of gases to be analyzed by the FTIR are stored in the instrument""s memory, and then those reference spectra are compared with the spectra of the sample gases during analysis. Subsequently, a method and apparatus for continuously withdrawing and sampling automobile emissions is disclosed in U.S. Pat. No. 5,138,163. That technique is sufficiently accurate for testing a sample of exhaust from traditional internal combustion engines.
One of the chief problems faced in sampling exhaust from near-zero emission vehicles is obtaining a dry sample. Any moisture in the line can significantly alter test data. As such, it is imperative that water be removed so that the moisture will not interfere with the FTIR readings. Some methods for obtaining a satisfactory sample include heating the gas itself to a temperature in excess of 100xc2x0 C. in order to maintain any water present in a vapor state, diluting the gas flow with the addition of large quantities of a non-reactive gas such as nitrogen, or passing the gas though a bank of desiccants to dehydrate it. All three of these methods have drawbacks. In the case of heating the gas to temperatures in excess of 100xc2x0 C., any reference or comparative samples also have to be heated to the same temperature to achieve an accurate comparison. Furthermore, even when maintained in a vapor state, the moisture may provide interference with certain low level FTIR measurement analysis. Diluting the gas with large quantities of a non-reactive gas decreases the level of sensitivity of the sample that can be obtained due to the dilution of the sample contents, thus providing a less accurate analysis. Also, dilution requires the presence of large tanks containing the diluting gas, making a compact system difficult to achieve. Alternatively, if ambient air is used in the dilution process, the pollutants in the ambient air may have an adverse effect on pollutant measurements when dealing with near-zero emission vehicles. And finally, passing the sample through a desiccant bank often removes gaseous components that are desirable for testing along with the water vapor.
The most recent technological advances in the art of moisture removal include the use of selectively permeable materials to remove water vapor via osmosis. For instance, U.S. Pat. No. 5,042,500 discloses a drying sample line for coupling a patient""s expiratory gases to a gas analyzer. The drying sample line comprises concentric tubes wherein the innermost tube is fabricated from a perflourinated polymer material sold as Nafion(copyright). The perflourinated polymer material exhibits high permeability to water vapor but does not readily pass other gases. The expiratory gas is drawn through the inner tube and, simultaneously, dried air is made to pass through the outer tube in a counterflow direction relative to the expiratory gases. Because of the properties of the perflourinated polymer material, water vapor (i.e., moisture) contained in the expiratory gas being coupled to the analyzer passes through the wall of the tube and into the dried air stream. Consequently, the water vapor is removed from the expiratory gas mixture being applied to the analyzer. There are existing products on the market that employ in-line systems utilizing perflourinated polymer tubing for drying gas streams.
While it is known to remove moisture from gases utilizing selectively permeable materials in fields such as medicine and in exhaust gases, no system exists that is both compact and efficient enough to provide the level of water removal required to allow for accurate testing onboard a moving near-zero emission vehicle. More particularly, a need exists for a cost effective and compact apparatus to remove moisture in sufficient quantities to allow for testing of exhaust gases while a near-zero emission vehicle is operating under standard road conditions, out of the lab and in its normal operating environment.
Another key testing data point relating to near-zero emission vehicles is comparison of the vehicle emission or exhaust with that of the ambient atmosphere. It would be extremely beneficial to be able to measure the actual level of pollutants in the ambient air through which the vehicle is travelling, and compare that to the level of pollutants being emitted by the vehicle. Presently, no device exists for real-time comparison of the level of pollutants in the vehicle exhaust to those found in the ambient atmosphere while the vehicle is travelling. For instance, in those urban environments where the level of ambient pollutants in the atmosphere is high, such high levels may distort the measurements being recorded concerning the vehicle exhaust. Therefore, a system which shows the level of pollutants in the atmosphere and is able to compare that to the level of pollutants being generated by the vehicle, can actually prove that the vehicle is producing a negative level of emissions. Where real-time analysis of both the effluent exhaust gases from a near-zero emission vehicle and the ambient air in which that vehicle is operating is required, it is essential that a compact and efficient system be available that will remove the moisture from both gas streams for proper FTIR analysis and provide the requisite feedback mechanisms to record and display the data.
Although conventional systems may detect pollutant levels, there remains an unmet need for a system that is compact enough to be placed on-board an automobile and that is able to measure the pollutant levels in a vehicle exhaust and compare those levels to the ambient atmosphere. That need is only heightened with the advent of near-zero emission vehicles.
In addressing the needs and deficiencies of the prior art, a system for sampling and measuring vehicle emissions, and comparing the results of the vehicle emissions to ambient air is provided.
More particularly, the vehicle emission sampling and measurement system of the present invention comprises both an intake for collecting an emission source and an intake for collecting ambient air. Both intake sources are coupled to analyzers that are disposed in the vehicle. The analyzers evaluate the chemical content of the emission source and the ambient air and provide corresponding electrical signals to a data processor. The signals corresponding to the chemical content of the emission source and the ambient air may then be compared and displayed on a screen connected to the processor.
Additionally, the vehicle emission sampling and measurement system may further comprise a water removal system for drying the gas streams prior to analysis in the analyzers. This water removal system may comprise a plurality of drying tubes coupled together in series, the drying tubes having a first flow path for the gas being sampled and a second flow path for a purge gas. Furthermore, the water removal system may comprise a series of heating and cooling stages wherein the efficiency of the drying tubes is increased. The analyzers may comprise Fourier transformer infrared spectrometer devices wherein the constituent chemical components of the gases are analyzed on a continuous real-time basis. In such a system, both the vehicle emissions and the ambient air are continuously gathered, analyzed and compared, and the results are stored and displayed in a real-time format.
A more complete understanding of the emissions sampling and measurement system will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly.